Particulate filters are utilized to remove particulate matter from an engine's exhaust flow. After an extended period of use, however, the particulate filter can become overloaded with particulate matter, creating a risk for filter damage and reducing engine performance. The collected particulate matter can be removed from the particulate filter through a process called regeneration.
Two different regeneration strategies are known, including active regeneration and passive regeneration. Active regeneration is the burning away of trapped particulate matter at high temperatures, typically in excess of 600° C. These temperatures can be periodically achieved through engine control, electric grids, and fuel fired burners located upstream of the filter to heat the exhaust flowing through the filter. Passive regeneration involves the use of a catalyst to reduce an oxidizing temperature of the trapped particulate matter such that it can be continually burned away at a low temperature without the use of engine control, electric grids, and fuel fired burners.
When a machine is stationary, active regeneration is undesirable, as it can heat the exhaust system too high for the immediate environment. For example, if a machine was to stop and remain located over dry debris, it might be possible for the high regeneration temperature of the exhaust system to ignite the debris. Thus, when a machine is parked and idling for long periods of time, such as occurs during an overnight stay, active regeneration is generally disabled and/or prohibited.
Unfortunately, when the machine idles, the exhaust temperatures of the machine can be so low that the oxidation catalyst of a passive regeneration system performs poorly. That is, the catalyst only functions properly when the exhaust temperature is within a predetermined activation range (250-400° C.), and this range can be difficult and expensive to attain during extended idling. Thus, without operator intervention, passive regeneration may only be marginally successful at removing the trapped particulate matter during extended idling and, in some situations, may not work at all. When regeneration does not function properly, the particulate filter can become completely clogged, resulting in malfunction of the engine that requires immediate servicing.
One attempt at addressing the problems described above is disclosed by U.S. Patent Publication No. 2005/0284138 (the '138 publication) by Imai et al., published on Dec. 29, 2005. The '138 publication discloses a regeneration control method for use with a continuously regenerating trap (CRT). The CRT includes a diesel particulate filter (DPF), and an oxidation catalyst located upstream of the DPF. The oxidation catalyst converts NO from an engine's exhaust to NO2, which is then used to oxidize particulate matter trapped within the DPF. The NO2 oxidizes the particulate matter at a lower temperature than would otherwise be possible. As long as an activating temperature of the catalyst is maintained, regeneration of the DPF is occurring, and occurring at a rate corresponding to the exhaust temperature.
The regeneration control method of the '138 publication includes monitoring soot loading of the DPF, and classifying the soot loading into three or four different categories of increasing amounts. The method further includes monitoring a temperature of the exhaust. Based on the soot loading classification and the exhaust temperature, different regeneration strategies are employed. In one strategy, when the soot loading of the DPF is classified as high and the exhaust temperatures are low such as during extended idling, the exhaust temperature can be artificially elevated such that the catalyst is activated and passive regeneration is promoted. The exhaust temperatures are elevated through the use of multiple post fuel injections of the associated engine.
The system of the '138 publication may lack efficiency. Specifically, artificially elevating the exhaust temperatures during idling requires large quantities of fuel and, at an idling condition, the temperature must be maintained at the elevated state for long periods of time to remove all of the soot present within the DPF. Without further control over the regeneration process, time and fuel efficiency of the process may be low.
The disclosed exhaust system is directed toward overcoming one or more of the problems set forth above and/or other problems in the art.